Process for the extraction and recovery of aromatic hydrocarbons



Nov. 3, 1970 H. L. 'rHoMPsoN PROCESS FOR THE EXTRACTION AND RECOVERY 0F AROMATIC HYDROCARBONS Filed DBC. 5, 1968 MS E@ N VEN TO?.l Herbert Lyf/e Thompson A TTOR/VEYS United States Patent O U.S. Cl. 208-321 9 Claims ABSTRACT OF THE DISCLOSURE Process for the recovery of aromatic hydrocarbons utilizing the steps of solvent extraction, water washing of the raffinate phase, recovery and reuse of the wash water, and fractionation of the extract phase. Sulfolane is the preferred solvent and benzene is recovered as a preferred product stream.

BACKGROUND OF THE INVENTION The present invention relates to the solvent extraction of aromatic hydrocarbons from a hydrocarbon charge stream. More particularly, the present invention relates to the recovery of solvent from the rainate stream produced in the process of extracting aromatic hydrocarbons from a hydrocarbon charge stream. More specifically, the present invention relates to an improved process for the recovery of solvent from the raffinate stream by means of an improved water wash technique.

It is well known in the art that the non-aromatic hydrocarbon raffinate which leaves the extraction zone of an aromatic hydrocarbon extraction process contains contaminating quantities of solvent. This solvent which contaminates the raffinate stream must be recovered not only because it may interfere with subsequent raflinate processing or ultimate raffinate use, but also because continual loss of solvent is a prohibitive economic expense in a commercial aromatic extraction process utilizing modern technology.

A typical solvent which is utilized in commercial aromatics extraction plants and which may be recovered in accordance with the practice of this invention is a solvent of the sulfolane-type. This solvent possesses a five-membered ring containing one atom of sulfur and four atoms of carbon, with two oxygen atoms bonded to the sulfur atom of the ring. Genetically, the sulfolane-type solvents may be indicated as having the following structural formula:

Rz-(H-H--R3 wherein R1, R2, R3, and R4 are independently selected from the group comprising a hydrogen atom, an alkyl group having from one to ten carbon atoms, an alkoxy radical having from one to eight carbon atoms, and an arylalkyl radical having from one to twelve carbon atoms. Other solvents which may be included within the process are the sulfolenes such as 2-sulfolene or 3-sulfolene which have the following structures:

Other typical solvents which have a high selectivity for separating aromatics from non-aromatic hydrocarbons ice and which may be processed within the scope of the present invention are Z-methylsulfolane, 2,4dimethylsulfo lane, methyl 2-sulfonyl ether, 11-aryl-3-sulfonyl amine, 2-sulfonyl acetate, diethylene glycol, various polyethylene glycols, dipropylene glycol, various polypropylene glycols, dimethyl sulfoxide, N-methyl pyrollidone, etc. The specifically preferred solvent chemical which is processed within the scope of the present invention is sulfolane, having the following structural formula:

Because the typical solvents which are utilized in aromatic extraction are water soluble, it is the practice of the art to extract the solvent from the rafiinate stream by Contact with an aqueous stream in a subsequent water wash extraction means. The extraction of the solvent from the raffinate with water may be undertaken in any suitable liquid-liquid contacting means, as in a tower containing suitable packing such as Berl saddles or Raschig rings, or in a tower containing suitable trays, or in rotating disc contactor (RDC). The solvent may then be readily recovered from the aqueous solution by distillation.

It has been discovered in the commercial aromatics extraction units that the recovery of sulfolane-type solvent from the raffinate by extraction with water does not correspond to the recovery which is to be anticipated based upon solubility data, and the assumption of reasonable efliciency of the extractor. Thus, the loss of sulfolane in the raffinate product has been found to be from five to eight times as great as anticipated, and this loss is greatly above what is economically desirable.

SUMMARY OF THE INVENTION Therefore, it is an object of the present invention to provide a process for the extraction and recovery of aromatic hydrocarbons from a feed mixture containing aromatic and non-aromatic hydrocarbons with a sulfolanetype solvent.

It is another object of this invention to provide an improved process for the recovery of solvent from the raflinate stream utilizing water washing in a facile and economical manner.

It is a still further object of this invention to provide a process for the production of a rainate product stream from an aromatic extraction process which is substantially free of solvent contaminant.

Accordingly, the present invention provides a process for the extraction and recovery of aromatic hydrocarbons from a feed mixture containing aromatic and non-aromatic hydrocarbons with a sulfolane-type solvent which comprises the steps of: (a) introducing said feed mixture into a solvent extraction zone maintained under aromatic hydrocarbon extraction conditions including the presence of said sulfolane solvent sufficient to produce an extract phase comprising said solvent having aromatic hydrocarbons dissolved therein and a raffinate phase comprising non-aromatic hydrocarbons contaminated with small quantities of said solvent; (b) passing said extract phase into first fractionation recovery means under fractionation conditions suicient to produce a first distillate stream y comprising said aromatic hydrocarbons and a first bottoms fraction comprising lean solvent suitable for reuse in said extraction zone; (c) introducing said rafnate phase into a first wash zone in contact with hereinafter specified first wash water stream under conditions suicient to absorb at least a portion of said contaminant into the wash water stream; (d) withdrawing from said first wash zone a nonaromatic hydrocarbon stream having reduced contaminant content and first rich water stream containing solvent; (e) passing said non-aromatic hydrocarbon stream into a second wash zone in contact with a hereinafter specified second wash water stream under conditions sufiicient to absorb substantially all of the remainder of said solvent contaminant into the wash water stream; (f) removing from said second wash zone a non-aromatic hydrocarbon stream substantially free of said solvent contaminant and a second rich water stream containing solvent; (g) introducing said second rich water stream into a second fractionation zone maintained under fractionation conditions suicient to produce a second distillate stream comprising water substantially free of said solvent and a second bottoms fraction comprising water containing said solvent; (h) passing said second distillate stream into said second wash zone as the specified wash water therein; (i) passing at least a portion of said second bottoms fraction into the rst wash zone as the specied wash water therein; and (j recovering said first distillate stream of step (b).

In essence, therefore, it can be seen that the present invention utilizes a two-stage water wash technique of the raiinate stream which operates in conjunction with a separate water distillation means for the production of separate and distinct wash waters for use in the two-stage water washing technique. In addition, it can be readily seen that the present invention embodies the unique concepts of water reuse in a facile and economical manner.

DETAILED DESCRIPTION OF THE INVENTION As a broad general class, suitable feedstocks for the satisfactory practice of this invention include fluid mixtures having a sufficiently high concentration of aromatic hydrocarbons to economically justify recovery of these aromatic hydrocarbons as a separate product stream. The present invention is particularly applicable to hydrocarbon feed mixtures which contain at least 25% by weight aromatic hydrocarbons. A suitable carbon number range for the feedstock is from about 6 carbon atoms per molecule to about 20 carbon atoms per molecule and, preferably, from about 6 to 10 carbon atoms per molecule. One suitable source of feedstock is the debutanized reactor eluent from a conventional catalytic reforming process unit. Another suitable source of feedstock is the liquid by-product from a pyrolysis gasoline unit which has been hydrotreated to saturate olens and diolens thereby producing an aromatic hydrocarbon concentrate suitable for the solvent extraction technique described herein. Typically, the feedstock from a catalytic reforming process contains single ring (monocyclic) aromatic hydrocarbons comprising a Wide boiling mixture of benezene, toluene, and xylenes. These single ring aromatic hydrocarbons are also mixed with the corresponding paraflns and naphthenes Which have been produced from such a catalytic reforming unit.

As previously mentioned, the preferred solvent which may be utilized in the present invention is a solvent of the sulfolane-type as described hereinabove. Since this solvent is an article of commerce and is well known to those versed in the solvent extraction art, greater detail thereof need not be presented at this time.

The aromatic selectivity of the solvent can usually be enhanced by the addition of water to the solvent. Preferably, the solvents utilized in the practice of this invention contains small quantities of water in order to increase the selectivity of the overall solvent phase for aromatic hydrocarbons without reducing substantially the solubility of the solvent phase for aromatic hydrocarbons. The presence of water in the solvent composition further provides a relatively volatile material which is distilled from the solvent in the subsequent extractor-stripper following the extraction zone, more fully discussed hereinafter, to vaporize the last traces of non-aromatic hydrocarbons from the solvent stream by steam distillation. Aordillgly, the

solvent composition of the present invention contains from about 0.1% to about 20% by weight water and, preferably, about 0.5% to 1.0% by weight depending upon the particular solvent utilized and the process conditions at which the extraction zone and the extractor-stripper are operated.

The solvent extraction zone of the present invention is operated at elevated temperature and sufhciently elevated pressure to maintain the feedstock, the solvent, and any reux streams in liquid phase. Typically, suitable temperatures, when using sulfolane as the solvent, are within a range from about F. to about 400 F. and, preferably, from about 175 F., to about 300 F. Similarly, suitable preessures are generally within the range from about atmospheric pressure up to about 400 p.s.i.g. and preferably, from 50 to 150 p.s.i.g.

This invention also embodies the concept of displacement of non-aromatic hydrocarbons from the extract phase at the lower end of the extraction zone by utilizing the technique of a non-aromatic hydrocarbon containing reflux at that point. It is distinctly preferred that this reilux stream comprise relatively light non-aromatic hydrocarbons, but may contain significant quantities of aromatic hydrocarbons, e.g. from 30% to 60% by weight. In other Words, the extractive distillation column following the extraction zone is operated in such a manner that a reflux stream is obtained which comprises a concentrate of nonaromatic hydrocarbon components which were left in the extract phase from the extraction zone.

The amount of reflux introduced into the lower end of the extraction zone may be varied considerably depending upon the degree to which non-aromatic hydrocarbons are being rejected in the extraction zone. It is preferred that the relatively light non-aromatic reflux introduced into the lower end of the extraction zone be at least 10% by volume of the extract phase in order to effectively displace non-aromatic hydrocarbons from the extract phase into the raflinate phase.

The extractive distillation column following the extraction zone utilizes the extract phase as feedstock and is operated at moderate pressures and sufliciently high reboiler temperatures in order to Vaporize all of the nonaromatic hydrocarbon material and a portion of the aromatic hydrocarbons, water, and solvent out of the bottom portion of this column. It is preferred that this rst distillation column be operated substantially as a stripper column although fractionation or separation does, in fact, take place therein; that is, the extract phase be fed into this column at the upper portion thereof in order to provide maximum stripping to take place in the column. In order for extremely high purity aromatic hydrocarbons to be ultimately obtained, it is essential that the extractive stripper column be operated in a manner to prevent all except minute traces of non-aromatic hydrocarbons from being withdrawn in the bottoms product stream from the lower end of this column.

Typically, the extractive stripper Will be maintained under pressures from atmospheric to about p.s.i.g., although, generally, the top of the stripper column is maintained at from 7 p.s.i.g. to about 20 p.s.i.g. The reboiler temperature maintained in the extractive stripper is, of course, dependent upon the composition of the extract phase feed thereto and the solvent. The column is arranged to take only an overhead fraction and the bottoms fraction as separate product streams. Those skilled in the art, from a knowledge of the prior art and the teachings presented herein, are Well versed in the operation of an extractive stripper column of this type and, therefore, additional details thereof need not be presented here.

The aromatic and solvent recovery column is operated at low pressures and sufliciently high temperatures to distill the aromatic hydrocarbons overhead as a distillate fraction thereby producing a bottoms fraction comprising lean solvent which is generally suitable for reuse in the solvent extraction zone. Again, the precise choice of operating conditions depends upon the feedstock characteristics including aromatic hydrocarbon content and the composition of the solvent. Preferably, the top of the aromatic recovery column is operated at about 100 to about 400 mm. Hg absolute. These subatmospheric pressures must be employed in order to maintain a sufficiently low reboiler temperature to avoid thermal decomposition of the solvent, particularly when the solvent is of the sulfolane-type. Preferably, the reboiler temperature should -be maintained below about 360 F. when using saturated sulfolane as the solvent.

Returning now to the operation of the extractive stripper column: the overhead stream from the extractive stripper column is in the vapor state and comprises primarily non-aromatic hydrocarbons of the naphthene and/ or paraffin type. Typically, this vapor stream together with a vapor stream from a water stripper column, hereinafter described, are condensed in a common condenser thereby producing a combined hydrocarbon stream and a Water stream. It is this condensed hydrocarbon stream which is preferably utilized as reflux in the extraction zone inthe manner previously discussed.

Returning to the solvent extraction zone description: the raffinate leaves the aromatic extraction zone at an elevated temperature, is cooled, and passed into a first water wash column. This first Water wash column, typically, is a vertically disposed vessel containing conventional liquid-liquid contacting apparatus, such as Berl saddles and other packing material. The cooled raffinate stream enters the lower end of the column and passes upwardly in countercurrent fashion in Contact with a first wash water stream, the source of which is hereinafter discussed, which is introduced into the upper portion of the column. Suitable operating conditions are maintained in the first water wash column so that, preferably, at least a significant portion of solvent contaminant which was in the raffinate phase is absorbed into the water phase. Thus, a first rich water stream containing the extracted sulfolane is withdrawn from the bottom portion of the first water wash zone, and a hydrocarbon stream having a reduced solvent contaminant content is withdrawn from the upper portion of the first water wash column.

The hydrocarbon stream comprising the hydrocarbons of the raffinate phase, and having a significantly reduced solvent content, is then passed into a second water wash zone, similarly constructed to the first water wash zone, such that the hydrocarbon stream is countercurrently contacted with a second water wash stream, from a source hereinafter described, under conditions sufficient to produce a non-aromatic product stream substantially free of solvent as an overhead stream, and a second rich water stream containing extracted solvent which is Withdrawn from the second wash zone at the lower end thereof.

In the practice of the present invention the first and second rich water streams are handled in separate ways. The first rich water stream is withdrawn from the first wash zone and is passed into a Water stripper column which is operated as a steam stripper under conditions sufficient to strip out and remove residual hydrocarbons from the first rich water stream. The overhead from the water stripper column, containing a concentrate of hydrocarbons, is withdrawn as a vapor stream and admixed with the previously mentioned vapor stream from the extractive stripper column and commonly condensed as hereinabove described. The bottom portion of the water stripper comprises water containing sulfolane and is conventionally introduced into a steam generator wherein it is converted into steam for use in the aromatic and solvent recovery column previously mentioned. Therefore, in a preferred embodiment of this invention, the bottoms from the water stripper column are introduced as steam into the aromatic`recovery column for use as stripping steam therein.

The second rich water stream which is withdrawn from the second water wash column is passed into a separate fractionation column which is maintained under distillation conditions including reboiling of the bottoms and reiiux introduction into the top of the column. Operating conditions are maintained in this second rich water fractionation column, such as 230 F. and 20 p.s.i.a. in the bottom thereof, sufficient to produce a distillate fraction comprising water substantially free of solvent. The distillate fraction is then passed into the upper portion of the second wash column as the second wash Water in the manner discussed hereinabove. The bottom from the fractionating column containing water contaminated with significant quantities of sulfolane is introduced into the first wash zone as the wash water specified therein. In addition, a portion of the bottoms from the fractionation column in a preferred embodiment are passed through column reboiler means in indirect heat exchange with lean solvent from a source hereinafter specified. In other words, in a distinct and specific embodiment of this invention the heat for operating the second rich water fractionation column is obtained entirely by indirect heat exchange with hot lean solvent.

Returning now to the aromatic and solvent recovery column: the overhead from the recovery column comprises substantially pure aromatic hydrocarbons and steam as a vapor fraction. The vapor fraction is condensed into an aromatic hydrocarbon product stream which is separated from the condensed steam or condensate. The aromatic hydrocarbons are withdrawn and recovered as a separate product stream. The condensate is withdrawn and introduced into the second rich water fractionation column, preferably, in admixture with the second rich Water stream. The bottoms from the aromatic and solvent recovery column, as previously mentioned, comprises lean solvent suitable for reuse in the solvent extraction zone. This material is relatively hot and in a preferred embodiment of this invention is passed first into steam generation means for the conversion of the bottoms from the water stripper column into steam by indirect heat exchange therewith and then subsequently passing the cooled lean solvent stream into the second rich water fractionation column reboiler means in the manner previously disclosed.

In summary, therefore, the present invention provides a method for the extraction and recovery of aromatic hydrocarbons which encompasses a novel Water handling scheme operating in conjunction with a novel raflinate Water wash technique so that not only may high quality aromatic hydrocarbons be produced, but also a non-aromatic hydrocarbon product streamwhich is substantially free of solvent contaminant. It is to be noted that the water circuit is arranged so that contaminating quantities of nonaromatic hydrocarbons are not introduced into the aromatic recovery column which if permitted to happen would contaminate and lower the purity of the recovered aromatic hydrocarbons. It is also to be noted that the water circuit of the present invention permits maximum recovery of the solvent together with extremely high utilization of heat so that significant economy of operation may be realized.

The invention may be more fully understood with reference to the appended drawing which is a schematic representation of apparatus for practicing one embodiment of the invention.

DESCRIPTION OF THE DRAWINGS Referring now to the drawing, a hydrocarbon-feedstock containing aromatic hydrocarbons and non-aromatic hydrocarbons, such as the desired product from a conventional catalytic reforming unit, comprising benzene, toluene, and xylene mixed with corresponding naphthenes and parafiins enters the system via line 10 and introduced into solvent extraction zone 11. Aqueous sulfolane as the lean solvent enters extractor 11 at an upper portion thereof via line 12 and a relatively light non-aromatic hydrocarbon reflux, from a source hereinafter described, enters extractor 11 at the lower end thereof via line 13. The raffinate stream comprising a concentrate of non-aromatic hydrocarbons contaminated with, say, from 1% to 5% by volume sulfolane is Withdrawn from extractor 11 via line 28 for further processing in accordance with the practice of this invention more fully developed hereinbelow.

An extract phase comprising sulfolane solvent having aromatic hydrocarbons dissolved therein and which is contaminated with small amounts of non-aromatic hydrocarbons, such as the corresponding naphthenes and paraffins, is withdrawn from extractor 11 via line 14, admixed with additional lean solvent from line 15, and the total admixture passed into extractive stripper column 17 via line 16. Sufiicient separation or distillation conditions, as previously mentioned, are maintained in extractive stripper 17 to produce a bottoms fraction comprising solvent having dissolved therein the desired aromatic hydrocarbons, such as benzene, toluene, and xylene, said bottoms being removed from distillation column 17 via line 20.

The distillation conditions in extractor stripper 17 are also sufficient to produce a distillate or overhead fraction comprising aromatic hydrocarbons, solvent, and essentially all of the non-aromatic hydrocarbons. This overhead vapor fraction is withdrawn from stripper 17 via line 18, admixed with an overhead vapor fraction from a water-stripper, more fully developed hereinbelow, from line 19, condensed for the removal of water by means not shown, and passed via line 13 as refiux in extractor 1l, as previously mentioned.

Referring now to the solvent and aromatic hydrocarbon stream in line 20: this material is passed into aromatic and solvent recovery column 21 which is maintained under conditions sufiicient to separate the aromatic hydrocarbons from the solvent phase. The aromatic hydrocarbons are concentrated as a distillate fraction in admixture with steam and removed from recovery column 21 via line 22. The operation of recovery column 21 includes the use of steam stripping on the column in order to remove the final traces of aromatic hydrocarbons from the solvent. Therefore, the lower end of column 29 includes inlet loci for the introduction of steam from a source hereinafter disclosed and the bottoms product from column 21 contains the desired solvent plus water in sufficient amounts such that this bottom material in line 12 comprises lean solvent suitable for reuse in the extraction zone.

The material in line 22 contains a concentrate of aromatic hydrocarbons and steam. This vapor stream is admixed with makeup water, as needed, if any, from line 23, condensed by means not shown, and passed via line 24 into accumulator 25. Accumulator 25 is maintained under conditions sufficient to separate the steam condensate from the aromatic hydrocarbons thereby producing an aromatic hydrocarbon product stream which is withdrawn from the system via line 26 and a steam condensate fraction which is withdrawn from accumulator 25 via line 27 for use in the raffinate water wash technique more fully developed hereinbelow.

Returning now to extractor 11: the raffinate phase which is withdrawn from extractor 11 Via line 28 contains primarily non-aromatic hydrocarbons together with small amounts of solvent and aromatic hydrocarbons. This rafiinate stream is introduced into first wash column 29 which may contain any suitable liquid-liquid contacting means, such as Berl saddles or Raschig rings or may comprise a tower containing suitable tray devices or containing a rotating disc contactor. A first water wash stream comprising the bottoms from a source hereinafter specified is introduced into the upper portion of first water wash column 29 via line 41. This first water wash stream passes in downward fashion in intimate contact with the upiiowing raffinate stream in such a manner that at least a significant portion of the contaminating solvent is adsorbed into the aqueous phase. The resulting wash rathnate stream comprising non-aromatic hydrocarbons having reduced sulfolane content leaves wash column 29 via line 34 and is passed into separate wash column 35 which may be identical to the configuration of wash column 29. A second wash water stream substantially free of sulfolane solvent and obtained from a source hereinafter specified is introduced into Wash column 35 via line 40. Suitable contacting conditions are maintained in wash column 35 so that substantially all of the remaining sulfolane solvent contaminant is extracted by the water wash stream thereby producing a washed raffinate product stream substantially free of solvent which is withdrawn from the system via line 36.

The bottom aqueous stream from wash column 35 contains water and the solvent which has been extracted. This second rich water stream is removed from wash column 35 via line 37, admixed with the water condensate from accumulator 25 in line 27, and passed into fractionating column 39 which is maintained under water distillation conditions including the use of bottoms reboiler 43, in a manner more fully discussed hereinafter. The operating conditions are sufficient to produce an overhead water fraction substantially free of sulfolane which is removed from column 39 via line 40 and passed into Wash column 35 in the manner previously discussed. The bottoms in column 39 comprise water which contains the extracted sulfolane solvent. This bottoms material is removed from column 39 via line 41 and passed into first wash column 29 at the upper portion therein as the first wash water stream specified. A portion of the material in line 41 is preferably passed via line 42 into reboiler 43 in indirect heat exchange with a heating medium in line 12, from a source hereinafter specified, in order to provide the requisite heat for water fractionation in column 39.

Returning now to iirst wash column 29: the aqueous stream accumulated in the lower portion of column 29 contains water which has contained therein a significant quantity of the sulfolane contaminant removed from the raffinate phase. It may also contain significant quantities of entrained non-aromatic hydrocarbons and in some cases a small amount of aromatic hydrocarbons. Accordingly, the material in line 30 is passed into water stripper column 31 which operates under hydrocarbon stripping conditions in such a manner that the overhead distillate fraction produced comprises water, non-aromatic hydrocarbons, aromatic hydrocarbons, if any, and a small amount of solvent. This overhead distillate fraction is removed via line 19 and admixed with the overhead from the extractive distillation column 17 from line 18 and processed in the manner previously described as reflux into extractor 11 via line 13. The bottoms material from water stripper 31 contains water and sulfolane solvent and is accumulated in steam generator 334 which operates not only to produce steam for stripping purposes in water stripper 31, but also produces a net product of steam which is passed via line 32 into aromatic and solvent recovery column 21 for use therein as stripping steam in the manner previously described.

As previously mentioned, the bottoms material from aromatic and solvent recovery column 21 comprises lean solvent suitable for reuse in the extraction zone and is withdrawn via line `12. 'In a preferred embodiment of this invention, the lead solvent in line 12 is passed first into steam generato-r 33 for the generation of steam therein and then passed into column 39 reboiler means 43 and from reboiler 43 into extractor 11 via line 1'2. Thus, by operating .in this manner, the heat content of the lean solvent stream is transferred first into steam generator 33 and then into Ireboiler 43 before being passed into extractor 11. Significant economy of operation is achieved by the practice of this preferred embodiment. It was also found by operating the present invention in the manner described that the rafiinate in line 36 will contain less than 5 parts per million of sulfolane solvent and, typically, will contain less than l part per million, e.g. 0.5 part per million of sulfolane. Still further, it was found that in a commercial version of this invention that as much as 50 to 100 pounds per day of sulfolane solvent could be saved over the processing schemes practiced by the prior art heretofore.

PREFERRED EMBODIMENT Therefore, from the description presented t-hus far, a preferred embodiment of lthis invention provides a process for the extraction and recovery of monocyclic aromatic hydrocarbons from 4a feed mixture containing aromatic and nonaromatic hydrocarbons which comprises the steps of: (a) introducing said feed mixture into a solvent extraction zone maintained under aromatic hydrocarbon extraction conditions including the presence of a sulfolanetype solvent suicient to produce an extract phase comprising said solvent having aromatic hydrocarbons dissolved therein and contaminated with non-aromatic hydrocarbons, and a raffinate phase comprising non-aromatic hydrocarbons contaminated with small quantities of said solvent; (b) passing said extract phase into an extractive distillation zone under conditions sufficient -to produce a first overhead fraction comprising a concentrate of nonaromatic hydrocarbons, and a first bottoms fraction comprising solvent having aromatic hydrocarbons dissolved therein; (c) passing said first bottoms fraction into fractionation means maintained under `distillation conditions including the presence of stripping steam from a source hereinafter specified sufficient to produce a second overhead fraction comprising a vapor of said monocyclic aromatic hydrocarbon and steam, and a second bottoms fraction comprising lean solvent suitable for reuse in said extraction zone; (d) condensing said second overhead vapor fraction thereby producing a product stream of monocyclic aromatic hydrocarbons, and an aqueous condensate stream; (e) introducing said raffinate phase into a first wa-ter wash zone in contact with a hereinafter specified first wash water stream under conditions sufiicient to adsorb at lea-st a portion of the solvent contaminant into the condensate stream; (f) withdrawing from said first wash zone a non-aromatic hydrocarbon stream having reduced solvent contaminant content, and a first rich water stream containing solvent and small quantities of non-'aromatic hydrocarbons; (g) passing said non-aromatic hydrocarbon stream into a second water wash zone in contact with a hereinafter specified Second wash water stream under conditions sufiicient to adsorb substantially all of the remainder of said solvent into the wash water stream; (h) removing from said second wash zone a non-aromatic hydrocarbon stream substantially free of said solvent contaminant, and a second rich water stream containing solvent; (i) introducing said first rich water stream into a stripping zone under conditions sufficient to produce a third overhead fraction comprising non-aromatic hydrocarbons, and a third fraction comprising water substantially free of hydrocarbon contaminant; (j) converting said third fraction into steam and injecting said generated steam into the fractionation means of step (c) as the specified source of stripping steam therein; (k) passing said second rich water stream into a fractionation zone maintained under distillation conditions sufficient to produce a fourth overhead stream comprising water having reduced solvent content, and a Vfourth bottoms fraction comprising water of increased solvent content; (l) introducing said fourth overhead stream into said second water wash zone as the specified Wash Water stream; (m) passing said fourth bottoms fraction into said first water zone as the specified wash water stream; and (n) recovering said product stream of step (d).

The invention claimed is:

1. Process for the extraction and recovery of aromatic hydrocarbons from a feed mixture containing aromatic and non-aromatic hydrocarbons with a sulfolane-type solvent which comprises the steps of:

(a) introducing said feed mixture into a solvent extraction zone maintained under aromatic hydrocarbon extraction conditions including the presence of said sulfolane solvent sufficient to produce an extract phase comprising said solvent having aromatic hydrocarbons dissolved therein, and a raiiinate phase comprising non-aromatic hydrocarbons contaminated with small quantities of said solvent;

(b) passing said extract phase into first fractionation recovery means under fractionation conditions suflicient to produce a first distillate stream comprising said aromatic hydrocarbons, and a first bottoms fraction comprising lean solvent suitable for reuse in said extraction zone;

(c) introducing said raffinate phase into a first wash zone in contact with hereinafter specified first wash water stream under conditions sufficient to adsorb at least a portion of said contaminant into the wash water stream;

(d) withdrawing from said first wash zone a nonaromatic hydrocarbon stream having reduced contaminant content, and first rich water stream containing solvent;

(e) passing said non-aromatic hydrocarbon stream into a second wash zone in contact with a hereinafter specified second wash water stream under conditions sufficient to adsorb substantially all of the remainder of said solvent contaminant into the wash water stream;

(f) removing from said second wash Zone a nonaromatic hydrocarbon stream substantially free of said solvent contaminant, and a second rich water stream containing solvent;

(g) introducing said second rich water stream into a second fractionation zone maintained under fractionation conditions sufficient to produce a second distillate stream comprising water substantially free of said solvent, and a second bottoms fraction comprising water containing said solvent;

(h) passing said second distillate stream into said second wash zone as the specified wash water therein;

(i) passing at least a portion of said second bottoms fraction into said first wash zone as the specified wash `Water therein; and

(j) recovering said first distillate stream of step (b).

2. Process according to claim 1 wherein said fractionation conditions of said second fractionation zone includes reboiling said zone by indirect heat exchange between said second bottoms fraction and said first bottoms fraction.

3. Process according to claim 1 wherein said sulfolanetype solvent has the structural formula wherein R is selected from the group consisting of hydrogen, alkyl radical having from 1 to 8 carbon atoms, aryl radical having from 1 to 10 carbon atoms, alkoxy radical having from 1 to 8 carbon atoms, and arylalkyl radical having from l to 12 carbon atoms.

4. Process according to claim 3 wherein said solvent comprises sulfolane.

5. Process for the extraction and recovery of monocyclic aromatic hydrocarbons from a feed mixture containing aromatic and non-aromatic hydrocarbons which comprises the steps of:

(a) introducing said feed mixture into a solvent extraction zone maintained under aromatic hydrocarbon extraction conditions including the presence of a sulfolane-type solvent sufficient to produce an extract phase comprising said solvent having aromatic hydrocarbons dissolved therein and contaminated with non-aromatic hydrocarbons, and a rafnate phase comprising non-aromatic hydrocarbons contaminated with small quantities of said solvent;

\(b) passing said extract phase into an extractive distillation zone under conditions sufiicient to produce a first overhead fraction comprising a concentrate of non-aromatic hydrocarbons, and a first bottoms fraction comprising solvent having aromatic hydrocarbons dissolved therein;

(c) passing said first bottoms fraction into fractionation means maintained under distillation conditions including the presence of stripping steam from a source hereinafter specified suicient to produce a second overhead fraction comprising a vapor of said monocyclic aromatic hydrocarbon and steam, and a second bottoms fraction comprising lean solvent suitable for reuse in said extraction zone;

(d) condensing said second overhead vapor fraction thereby producing a product stream of monocyclic aromatic hydrocarbons, and an aqueous condensate stream;

I(e) introducing said raffinate phase into a rst Water wash zone in contact with a hereinafter specified first Wash Water stream under conditions sufficient to adsorb at least a portion of the solvent contaminant into the condensate stream;

(f) withdrawing from said first Wash zone a nonaromatic hydrocarbon stream having reduced solvent contaminant content, and a first rich water stream containing solvent and small quantities of nonaromatic hydrocarbons;

(g) passing said non-aromatic hydrocarbon stream into a second water Wash zone in contact with a hereinafter specified second lwash `water stream under conditions suficient to adsorb substantially all of the remainder of said solvent into the wash water stream;

(h) removing from said second wash zone a nonaromatic hydrocarbon stream substantially free of said solvent contaminant, and a secondrich water stream containing solvent;

(i) introducing said first rich water stream into a stripping zone under conditions sufiicient to produce a third overhead fraction comprising non-aromatic hydrocarbons and athird fraction comprising water substantially free of hydrocarbon contaminant;

(j) converting said third fraction into steam and injecting said generated steam into the fractionation means of step (c) as the specified source of stripping steam therein;

(k) passing said second rich water stream into a fractionation zone maintained under distillation conditions sufiicient to produce a fourth overhead stream comprising water having reduced solvent content, and a fourth bottoms fraction comprising water of increased solvent content;

(l) introducing said fourth overhead stream into said second water wash zone as the specified wash water stream;

(m) passing said fourth bottoms fraction into said first water wash zone as the specified wash water stream; and

(n) recovering said product stream of step (d).

6. Process according to claim 5 wherein said distillation conditions of the fractionation zone of step (k) includes reboiling said zone by indirect heat exchange between said second bottoms fraction of step (c) and saidfourth bottoms fraction of step (k).

7. Process according to claim 5 lwherein said aqueous condensate stream of step (d) is injected as a feed stream into the fractionation zone of step (k).

8. Process according to claim 5 wherein said sulfolanetype solvent has the structural formula wherein R is selected from the group consisting of hydrogen, alkyl radical having from 1 to 8 carbon atoms, aryl radical having from 1 to l0 carbon atoms, alkoxy radical having from l to 8 carbon atoms, and arylalkyl radical having from 1 to l2 carbon atoms.

9. Process according to claim 8 wherein said solvent comprises sulfolane.

References Cited UNITED STATES PATENTS 3,179,708 5/ 1965 Penisten 208-321 3,209,047 9/ 1965 Young 20S-321 3,338,823 8/ 1967 Voetter 20S-321 3,338,824 8/1967 `Oliver 208-321 3,361,664 1/1968 iBroughton et al. 208-321 3,436,435 4/ 1969 Tassell 208-321 3,461,066 4/ 1969 Morris et al. 208-321 3,476,681 11/ 1969 Davies et al. 20S-321 HERBERT LEVINE, Primary Examiner U.S. Cl. X.R. 20S-325; 260-674 

